In manufacturing of semiconductor elements as an example, with the recent trend of higher density integration in semiconductor devices, wavelengths of energy sources for irradiation instruments used in fine processing, particularly those used in lithography, have become shorter and shorter, and now deep UV (300 nm or less) and KrF excimer laser (248 nm) have already been made into practical use, and ArF excimer laser (193 nm) is close to practical use. Further studies for exposure technology using F2 laser (157 nm), electron beams, extreme UV (EUV: 1 to 30 nm band) and the like has been promoted for the purpose of ultrafine fabrication of 100 nm or less. In resist compositions under development for these applications, various known acid generators are used, but use of these known acid generators causes various problems.
For example, when a diazodisulfone compound having an aliphatic alkyl group, which is presently used, is used as an acid generator, the compound has such problems that strong acid cannot be generated or acid generation efficiency is poor, whereas, use of a diazodisulfone compound having an aromatic group as an acid generator, also has problems such as poor solution stability. Further, when a sulfonium salt or an iodonium salt is used as an acid generator, there are also such problems that fine particles are easily formed due to poor solubility, storage for several weeks is difficult due to poor solution stability, and when said salt has a counter anion derived from trifluuoromethanesulfonic acid, easy variations in resist performances are caused; (e.g. variations in dimension, sensitivity, shape and the like) and thus a practically suitable acid generator has not been found.
Further, as a resist composition using an imidesulfdnate compound as an acid generator, the following resist compositions have been disclosed: use of a combination of poly(hydroxystyrene/styrene/tert-butyl acrylate) and N-trifluoromethylsulfonyloxy-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxyimide (see JP-A-7-209868); use of a combination of poly(p-hydroxystyrene/tert-butyl acrylate) and N-camphorsulfonyloxynaphthalimide or N-trifluoromethylsulfonyloxy-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxyimide [see H. Ito et al., ACS. Symp. Ser., 1995, vol.614 (Microelectronics Technology), p 21-34; H. Ito et al., J. Photopolym. Sci. Technol., 1996, vol. 9 (No. 4), p. 557-572; and JP-A-6-266112]; use of N-pentafluorobenzenesulfonyloxy-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxyimide (see JP-A-3-206458); use of a combination of poly(styrene/p-hydrbxystyrene/p-tert-butoxycarbonylmethoxystyrene) and N-benzenesulfonyloxysuccinimide (see JP-A 6-214395) and use of N-norbornanesulfonyloxy-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxyimide (see JP-A-2001-199955). However, these N-imidesulfonate compounds have such problems that the resist composition using these compounds is, due to asymmetric structure and high reactivity thereof, labile to moisture and the like, and thus gives a solution with poor solution stability, low acid generation efficiency and low sensitivity. In addition, a N-imidesulfonate compound having a counter anion derived from trifluoromethanesulfonic acid also has a problem such as easy variation in resist performances, similar to the above.
As an analogous compound to a bisimide compound of the present invention, for example, 2,6-bis(methanesulfonyloxy)benzo[1,2-c:4,5-c′]dipyrrole-1,3,5,7(2H, 6H)-tetrone [see Y. Imai et al., J. Polym. Sci. Polym. Chem. Ed., 1975, vol. 13 (No. 10), p. 2391-2396;-DE-A-19540107 and the like] has been reported. However, these compounds are, used as a raw material for a polyimide compound and not relates to an acid generator, and even if use of said, compouds as an acid generator is intended, they cannot be used due to extremely poor solubility in a resist solvent. Further, 3a,4,4a,7a,8,8a-hexahydro-2,6-bis(butanesulfonyloxy)-4,8-ethenobenzo[1,2-c:4,5-c′]dipyrrole-1,3,5,7(2H, 6H)-tetrone (see JP7A-11-258801) has also been reported. However, this compound was used as a cross-linking agent for a chemically amplified negative resist composition and not relates to an acid generator, and even if use of said compound as an acid generator is intended, it cannot be used due to low sensitivity, low resolution and poor profile.
Further, as other analogous compounds to a bisimide compound of the present invention, for example, 5,5′-oxybis[2-trifluoromethanesulfonyloxy-1H-isoindole-1,3(2H)-dione] and 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis[2-trifluoromethanesulfonyloxy-1H-isoindole-1,3(2H)-dione] (see JP-A-3-206458, JP-A-6-301200, JP-A-8-501890 and the like), and 5,5′-oxybis[2-(4-toluenesulfonyl)oxy-1H-isoindole-1,3(2H)-dione] (see JP-A-11-167199) have been reported as an acid generator for chemically amplified resist materials. However, these compounds cannot be practically used as a resist composition due to no solubility in a resist solvent generally used.
As described above, conventional acid generators practically used or studied have the following problems: an acid generated is weak; acid generation efficiency is insufficient; fine particles are easily formed due to poor solubility; use of said acid generator as a resist compositions occurs decomposition during storage due to poor solution stability resulting in variation in sensitivity or poor pattern formation; and a resist composition itself cannot be prepared due to little solubility in a resist solvent. Thus, development of a useful compound which can solve these problems and generates an acid in response to radioactive ray, is now demanded.